The present invention relates to a current evaluation circuit and a method for sensing an electric current. In particular, the present invention relates to a current detection device and a method for sensing an electric current on a measuring path, which carries an electric current corresponding to an electric current on a power path.
Although the present invention is described in relation with IGBT which have a sense terminal, the present invention can be used additionally also for any other cases of application in which a current is to be evaluated on a further current path which corresponds to the current on a power path.
Printed document U.S. Pat. No. 5,877,617 A discloses a circuit arrangement in which a load on a current path is fed with a current. In addition, the circuit arrangement comprises a further transistor which provides a current corresponding to this current for the load. The current which is provided by the further transistor is used for monitoring and evaluating the current flow for the load.
For the measurement and evaluation of the current through a semiconductor switch, bipolar transistors having an insulated gate (IGBT) are also known in which, at an additional sense terminal, a current is provided which is proportional to the main current through the semiconductor switch. The current from the sense terminal is then lower by an approximately constant factor than the main current on the emitter path of the IGBT.
The circuit arrangement for evaluating the current in the sense path of such an IGBT must then be dimensioned for the maximum on-period of the IGBT and also for the maximum current occurring. In this context, relatively large currents can occur also on the sense path, especially in the case of a fault.
There is, therefore, a requirement for a device and a method for current detection which enables currents to be detected with high accuracy over a relatively wide measuring range.